Okay, this is a classic problem with inrush current, especially with multiple computers starting simultaneously. Let's break down the likely causes and potential solutions

1. Is this behavior likely caused by excessive inrush current during PC startup?

Yes, almost certainly. Here's why: Inrush Current (also called In-rush Current, Surge Current, or Input Surge Current)

When a device with a capacitor-based power supply (like a PC) is initially powered on, the capacitors need to charge. This creates a very short but very high current demand. It's like a sudden surge of electrons flooding into the power supply. This spike can be many times higher than the normal operating current.

Cumulative Effect

When multiple PCs start simultaneously, their inrush currents add up. This combined inrush current can easily exceed the trip rating of the MCB.

MCB Characteristics

MCBs (Miniature Circuit Breakers) are designed to trip based on time and current. They have a characteristic curve that dictates how quickly they will trip at different overload levels. The initial surge pushes the current level far above the rated value, causing the MCB to trip very quickly. "C" type MCBs (as you have) are specifically designed to tolerate a higher surge for a short time (e.g. for starting electric motors) - but even this tolerance has its limits.

Spark Indication

The "visible spark" in Case 2 is a good indicator of a large fault current – confirming an overcurrent scenario.

Disconnected PCs

The fact that the tripping stops when PCs are disconnected and thus not drawing any inrush current reinforces that the issue stems from the PCs.

2. What are the recommended solutions to prevent these nuisance trips?

Here's a multi-faceted approach to address the issue

A. Immediate/Short-Term Solutions:

Staggered Startup

This is the most straightforward and often the most effective solution. Implement a procedure to power on the PCs in stages. For example, divide the PCs in each sub-circuit into groups and turn them on one group at a time, waiting a few seconds between each group. This spreads out the inrush current over a slightly longer period, reducing the peak demand. You can do this manually or with software that controls power states (Wake-on-LAN can be problematic if misconfigured and all PCs are sent a wake command at the same time).

Turn off Unused PCs

If you have some PCs that are not used all the time, keep them turned off.

Upgrade MCBs with Caution (and Calculation)

This should be done with caution and only after consulting a qualified electrician. You might consider upgrading the MCBs to a higher current rating (e.g., from C32 to C40). However, you

must ensure that the wiring and other components in the circuit are rated to handle the higher current. Upgrading without checking this can create a fire hazard. It's also crucial to understand that simply increasing the MCB rating doesn't solve the underlying problem; it just increases the threshold before tripping, potentially putting stress on the wiring. Crucially, make sure the upstream protection is adequate (i.e. your C100 should trip before anything upstream does). Replace MCBs with ones designed for higher inrush

As an alternative to increasing the current rating of the MCBs, consider replacing them with ones designed to better handle inrush current. Some manufacturers offer MCBs specifically designed for inductive loads or equipment with high inrush currents. These MCBs have a different tripping curve that allows for short duration overloads without tripping, but still provides adequate protection against sustained overcurrents.

B. Long-Term/More Robust Solutions



Soft Starters/Inrush Current Limiters

Install inrush current limiters on the power supplies of the PCs. These devices gradually increase the voltage applied to the power supply, limiting the initial inrush current. They're available as standalone units that plug into the wall or as components that can be integrated into the PC's power supply (more complex). This is often the best solution in the long run, especially for larger installations.

Power Distribution Units (PDUs) with Sequential Startup

These PDUs have the ability to power on outlets in a sequence with a defined delay between each outlet. This achieves the same effect as staggered startup but is automated. Many PDUs also offer remote monitoring and control capabilities.

Higher Quality Power Supplies (PCs)

Some PC power supplies are designed with better inrush current limiting circuits. If you're replacing PCs, consider models that have this feature. Look for power supplies that meet 80+ certification requirements - often a sign of a higher quality power supply.

Investigate UPS (Uninterruptible Power Supply)

A UPS can provide clean, consistent power and potentially mitigate inrush current problems (depending on the UPS design). However, be sure to select a UPS with enough capacity to handle the total load and inrush of all the connected PCs. A "line interactive" UPS might not be sufficient for this situation. An "online" or "double-conversion" UPS provides the best isolation from input power issues.

Dedicated Circuits

In Case 2, 30 PCs on two C32 MCBs is a relatively high density. Consider adding dedicated circuits with their own MCBs to reduce the load on each circuit.

Detailed Load Analysis and Electrical System Review

This is crucial. Hire a qualified electrician to perform a thorough load analysis of your electrical system. They can: Measure the actual inrush current of the PCs. Verify that the wiring and other electrical components are adequately sized for the load. Check the upstream protection (the C100 and anything further upstream). Ensure that the electrical system meets local codes and regulations.

Important Considerations



Safety First

Electrical work can be dangerous. If you are not a qualified electrician, do not attempt to modify the electrical system yourself.

Code Compliance

Any electrical modifications must comply with local electrical codes.

Document Everything

Keep a record of any changes you make to the electrical system.

Consider the Type of Load

Are these gaming PCs with high-end graphics cards? These will draw significantly more power (and thus have higher inrush currents) than basic office PCs.

Power Factor Correction

Some PC power supplies have poor power factor. Power factor correction (PFC) can improve the efficiency of the power supply and reduce the overall current draw, but it may not directly address the inrush current issue.*

Monitor after making changes: After implementing any solution, monitor the system to ensure that the tripping issue is resolved and that the electrical system is operating safely.By systematically addressing the inrush current problem using a combination of the above solutions, you should be able to prevent nuisance tripping and ensure a stable power supply for your computer equipment. Good luck! Flag for review